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Busy beavers and ballooning spiders signify fall


BeaversSpiders_092210.MP3 (1).mp36.16 MB

 Chel Anderson is a botanist and plant ecologist for the Minnesota Department of Natural Resources. She lives here in Cook County and joins us periodically to talk about phenology, or what’s going on in the woods right now. Welcome back, Chel.

Anderson: Thanks, glad to be here.
Well, now that we’re into autumn officially, can winter be far behind? That’s a rhetorical question. That brings me to thoughts of beavers.
Anderson: One of the things that often happens at this time of year, because the trees, many of the trees, have lost all their leaves, and the trees aren’t taking up nearly as much water from the ground, so when we have our fall rains, that often helps raise the level of our rivers and lakes, because more water can just move right through the ground and into lakes and streams and replenish ground water, so that always reminds me of why beavers might be out being very busy with their dams, right, because water levels can be changing, can be rising. So, dams that might have been sufficient over the summer, especially this year when it was so dry, are now being tested more, and beavers are never comfortable with water running over their dams, or through them, but they’re never really satisfied if their dams have a lot of water running over them. I think it makes them a little uncomfortable. Right now is a very busy time for beavers, both getting their dams really well solidified, built up higher if necessary to take advantage of raising the water level in a pond to give even more assurance that it won’t freeze out to the bottom. So, they’re going to be building up their dams, which includes not just bringing woody material to the dam and interlacing it all together, but also literally digging out with their front feet whatever clay or muck they can from the bottom of their pond and carefully bringing it over and pushing it and patting it and stomping it into and over their dam to seal it up so water moves through it, but very slowly, at a very slow rate. They’re doing the same thing with their lodge. So, they’re preparing where they’re going to spend the winter, so they’re bringing woody material, piling that, and as they go, they do this layering and mortaring of the wood with their muddy mortar. Since the days are shorter now, beavers tend to be out more during the daylight hours, so you don’t even have to go out at night to watch them. And, it’s fascinating to get to watch them, how they do their construction and how amazingly strong they are at carrying sometimes big clods of mud or root balls up on to these steep slopes up to the tops of their lodges, just walking on their hind feet and hefting these huge blobs up onto their lodges. It’s a great form of entertainment, if anything else. In addition to that, they also have to be thinking about the huge food cache that they’re going to make out right in front and connect to wherever they’re going to lodge for the winter. And, they’re starting with material like alder, a variety of shrubs that they’re going to be able to get down below the surface, because they build their pile from the bottom up. So, they go down and plunge those cuttings from the shrubs and smaller tree branches into the muck of the bottom of their beaver pond, and then they build the pile up by wedging more stuff into that, and it just becomes this big jumbled pile that is holding together because it’s so stuck together, and it’s fastened to the bottom, so it can’t go whisking away if the river comes up.
What’s all this about ballooning spiders?
Anderson: Well, I really thought that would be kind of fun to talk about, because it’s something I really look forward to trying to catch a glimpse of in the fall. Especially on those days when it’s the nicest to be out in the fall, you know, clear, bluebird-blue sky days where the temperatures may be getting up to 50 or even higher some days, and there’s not a huge wind, but a nice, kind of steady breeze. Those are the kinds of days in the fall that spiders use to disperse. Most all critters have to have some way of moving away from each other, because, if you’re a female spider and you’ve hatched out 2 or 3 broods of hundreds of little spiders, even if just a few of those from each brood make it, you can’t all live right there, there isn’t enough for everyone. So, you’ve got to move out and move to new places and spread the genes around, so that we create a lot of genetic diversity within the population. So, there are evolutionary advantages to moving.
So, they can’t move far enough away by walking. They have to catch a plane, right?
Anderson: Exactly. They have this just amazing thing they do, which, a good place to see would be to go out to somewhere that is an opening, that has a good sunny spot where the breeze is breezing through, and look on the tops of whatever the vegetation is, and try to watch for spiders out on the tops of those. And how they do this is they throw out their silk in a long line and they just keep letting it go out, and the breeze, of course, will pick that up. And they let it out and they let it out and then at some point, I don’t know how they decide or if it’s serendipitous, but they just take off on that silk like a kite, as if it were a kite or a balloon. That just takes them right up into the air, lofts them way up high, and there’s even been some collecting done in what’s called the Aolian sphere. That’s maybe not a common usage word, but that’s the very upper part of the atmosphere, and some spiders actually make it way up high, tens of thousands of feet high. So, ballooning spiders are definitely a potential thing to look for.
Well, now some spiders are pretty good size. Can they do that, too?
Anderson: No, they can’t. But, the small ones can. So, it’s worth paying attention to if you’re out on a nice hike somewhere and you come to one of those nice sunny openings on the kind of day I described. Just keep your eyes out. Or, if you get wound up in a bunch of gossamer, maybe you’re in someone’s flight path.
Chel Anderson, DNR botanist and plant ecologist, thanks for helping us understand what’s going on around us this fall, particularly those ballooning spiders.
Anderson: You’re very welcome.